ISHS Acta Horticulturae 234: VII International Symposium on Virus Diseases of Ornamental Plants
CHRYSANTHEMUM PHLOEM NECROSIS: MICROSCOPY OF THE PUTATIVE PATHOGEN |
| Authors: | H. W. Israel, R. Kenneth Horst, Robert J. McGovern, S. O. Kawamoto, Karen F. Weaber, Susan J. Bucci, E. Paduch-Cichal |
| Abstract:
Recent studies in our laboratories have causally implicated mycoplasmalike organisms (MLOs) in the etiology of chrysanthemum phloem necrosis (CPN). For the present study we used combined light and electron microscopy to locate and describe suspect structures, which may represent the putative pathogen, in vascular tissues from symptomatic florist's chrysanthemum 'Pink Marble' and 'Showoff', from scions of initially unaffected 'Fanfare' and 'Bonnie Jean' grafted to diseased 'Pink Marble' stocks, from periwinkle that showed classical yellows symptoms after it had been bridged via dodder to diseased 'Showoff', and in maintenance cultures of organisms isolated from diseased 'Showoff' or 'Velvet Ridge'. The observations present a clear, albeit circumstantial, association of three distinct bodies, rarely seen in large numbers in chrysanthemum, with CPN: i) Some bodies, which closely resemble conventional spheroid MLOs that contain internal structures similar to ribosomes and DNA fibrils, were seen in sieve elements and phloem and xylem parenchyma; ii) other bodies, which resemble certain spheroid MLOs that bear internal dense cores, were seen only in chrysanthemum root and shoot apices; and, iii) still other bodies, which resemble filamentoid MLOs of varied size and shape observed in maintenance cultures from chrysanthemum, were seen in a variety of host cell types. In chrysanthemum, members of one or more of the three classes of bodies, which may be developmentally and functionally related, were always seen in infected plants but not always in anatomically affected cells. | |
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